III-V semiconductor materials are rapidly developing for use in electronic and optoelectronic applications. Many III-V semiconductor materials have direct band gaps, which make them particularly useful for fabricating optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes (LDs). Specific III-V semiconductor materials, such as gallium nitride (GaN), indium nitride (InN), aluminum nitride (AlN) and their alloys (commonly referred to as the III-nitrides), are emerging as important materials for the production of shorter wavelength LEDs and LDs, including blue and ultra-violet light-emitting optoelectronic devices. Wide band gap III-nitrides may also be utilized for high-frequency and high-power electronic devices due to the III-nitrides' ability to operate at high current levels, high breakdown voltages and high temperatures.
One widely used process for depositing III-V semiconductor materials is referred to in the art as metal-organic chemical vapor deposition (MOCVD). In MOCVD processes, a substrate is exposed to one or more gaseous precursors in a reaction chamber, which react, decompose, or both react and decompose in a manner that results in the epitaxial deposition of the group III-V material on a surface of the substrate. MOCVD processes are often used to deposit III-V semiconductor materials by introducing both a precursor containing a group III element (i.e., a group III element precursor) and a precursor containing a group V element (i.e., a group V element precursor) into the reaction chamber containing the substrate. This results in mixing of the precursors (i.e., the group III element precursor and the group V element precursor) before their exposure to the surface of the substrate.
Deposition of III-V semiconductor materials using a MOCVD process involves a balance between growth rate at the surface of the substrate and compound formation in the vapor phase. Specifically, mixing of the group III element precursor and the group V element precursor may result in the formation of particles that consume the precursors that are otherwise used to form the III-V semiconductor material on a suitable growth substrate. Consumption of available precursors during the MOCVD process creates difficulties in controlling the growth rate, thickness and composition of the III-V semiconductor material, especially in large reaction chambers. Variation in the thickness and composition of the III-V semiconductor material formed using the MOCVD processes may negatively affect throughput and yield of devices having a specific emission wavelength, such as wavelength-specific LEDs. Furthermore, deposition rates of III-V semiconductor materials formed by MOCVD processes are generally low, thus decreasing throughput and increasing cost per wafer.
Atomic layer deposition (ALD) is a process used to deposit conformal material with atomic scale thickness control. ALD may be used to deposit III-V semiconductor materials. ALD is a multi-step, self-limiting process that includes the use of at least two reagents or precursors. Generally, a first precursor is introduced into a reactor containing a substrate and adsorbed onto a surface of the substrate. Excess precursor may be removed by pumping and purging the reactor using, for example, a purge gas. A second precursor is then introduced into the reactor and reacted with the adsorbed material to form a conformal layer or film of a material on the substrate. Under select growth conditions the deposition reaction may be self-limiting in that the reaction terminates once the initially adsorbed material reacts fully with the second precursor. Excess precursor is again removed by pumping and purging the reactor. The process may be repeated to form another layer of the material, with the number of cycles determining the total thickness of the deposited film.
III-V semiconductor materials formed utilizing ALD processes may be of a higher crystalline quality than those formed by conventional MOCVD processes. ALD processes may allow for greater control of precursor incorporation into the deposited crystalline material and consequently a greater control of the composition of the crystalline material formed, e.g., of the III-V semiconductor material formed by such ALD processes. Such stringent control of the composition of the III-V semiconductor material may be of consequence in light-emitting devices, for example, to ensure a uniform emission wavelength between light-emitting devices fabricated on a single growth substrate and between light-emitting devices from growth substrate to growth substrate.
However, the growth rate of III-V semiconductor materials by conventional ALD processes is relatively low in comparison to that of MOCVD. Furthermore, high throughput of III-V semiconductor materials by conventional ALD requires increased load sizes that make purging excess precursor and purge gas out of the reactor difficult. Thus, currently available ALD reactors are often configured for single wafer processing, leading to low throughput and high cost per wafer of III-V semiconductor materials by ALD.
Recently, ALD methods and systems have been developed in which each precursor is provided continuously in spatially separated regions, and each precursor is introduced to the substrate as the substrate is moved through each precursor in succession. Such processes are often referred to in the art as “spatial ALD” or “S-ALD.”